Wind-powered electrical generators in current use commonly employ a horizontal-axis, propeller-like wind turbine to capture power from air flowing parallel to the rotational axis of the turbine blades. However, as the wind direction can change, such turbines need to be mounted so that they may pivot about a vertical axis in order that they may face directly into the wind. The blades of such a turbine are generally three in number and extend radially from a central hub, to which they are attached at one end, to form a propeller that is driven by the wind. Generally the cross sectional area and pitch angle of each blade vary with increasing distance from the hub. At least one crane is required to assemble and erect such a wind turbine, unless it is sufficiently small to be assembled by hand.
The present invention is concerned with a design of turbine known as a Darrieus wind turbine. In such turbines, the blades rotate about an axis perpendicular to the wind direction, and as such can be driven by wind from any direction, without the need for re-orientation. The blades of a Darrieus turbine are generally attached to a rotor shaft at both ends, and their cross-section is generally constant in shape and pitch angle.
In U.S. Pat. No. 1,835,018, G. J. M. Darrieus disclosed a three-bladed wind turbine mounted on a vertical rotating shaft. Since that time, the Darrieus turbine has received substantial attention as an effective means of power generation.
Various configurations of generator and blades have been tried in Darrieus turbines, but presented disadvantages in requiring cranes for the purposes of installation, especially when the number of blades exceeds two. The number of blades is generally three, as shown for example in U.S. Pat. Nos. 1,835,018 and 4,449,053, as they provide advantages of reduced torque fluctuations, improved appearance and improved rotational balance.
In the installation of Darrieus turbines, cranes have generally been used to lift and attach blades at a significant height from the ground, requiring expensive equipment and teams of workers. It is also necessary in this case to provide extra strength in the blades, and or a custom-built lifting frame, to prevent blade distortion during installation.
U.S. Pat. No. 4,449,053 discloses a vertical axis wind turbine of the Darrieus type with guy ropes, means for lubricating an upper bearing, and a hinged tower, for assembly on the ground before erection. This proposal has the advantage of enabling the assembly of blades to the turbine in closer proximity to the ground before raising the turbine, but it will readily be seen that the assembly of three evenly spaced blades, as shown in the patent, would nevertheless require joints to be completed at significant height above the ground, in other than very small turbines. Additionally, no means is provided for unloading and positioning the parts of the turbine for assembly, and so a crane is still required in some form.
U.S. Pat. Nos. 5,375,324 and 5,499,904 disclose similar vertical axis turbines but do not provide means for assembly without the use of cranes.
U.S. Pat. No. 5,252,029 discloses a vertical axis turbine with a hinged base and a method of erection without the use of cranes, but relies for support on guy wires and anchors, and provides no means to address the problem of attaching blades while the turbine is on the ground. This patent has the disadvantages that guy wires occupy space over a considerable area, and that it is necessary, as described above, to use a crane for attachment of blades to the turbine, except where the turbine is of a small size, and except where the number of blades is less than three.